Dye-sensitized solar cell

ABSTRACT

According to an aspect of the present invention, there is provided a dye-sensitized solar cell including: a first substrate having a light-transmitting property; a semiconductor electrode containing a sensitizing dye and arranged with a first surface thereof facing the first substrate; a first collector electrode arranged on a second surface of the semiconductor electrode; an insulating layer arranged in contact with the first collector electrode; a catalytic electrode layer arranged with a first surface thereof facing the insulating layer; a second substrate arranged on a second surface of the catalytic electrode layer; and an electrolyte material incorporated in the semiconductor electrode, the first collector electrode and the insulating layer. This dye-sensitized solar cell becomes lower in internal resistance without the need to provide a light-transmitting collector electrode and the like to the light-transmitting first substrate on the light incident side.

TECHNICAL FIELD

The present invention relates to a dye-sensitized solar cell fordirectly converting light energy into electrical energy, in particular,of the type having a lower internal resistance without the need toprovide a light-transmitting collector electrode and the like to alight-transmitting substrate on the light incident side.

BACKGROUND ART

Solar cells utilizing single-crystal silicon, polycrystalline silicon,amorphous silicon, HIT (Heterojunction with Intrinsic Thin-layer) formedby varying combinations thereof have currently been put to practical useand become major techniques in solar power generation technology. Thesesilicon solar cells show excellent photoelectric conversion efficienciesof nearly 20%, but require high energy costs for material processing andhave many problems to be addressed such as environmental burdens andcost and material supply limitations.

On the other hand, dye-sensitized solar cells have been proposed byGratzel et al. in Japanese Laid-Open Patent Publication No.Hei-01-220380 and Nature (vol. 353, pp. 737-740, 1991) and come toattention as low-priced solar cells. This type of solar cell is providedwith a porous titania semiconductor electrode 3 supporting thereon asensitizing dye 31, a counter electrode 6 and an electrolytic layer 81interposed between the semiconductor electrode 3 and the counterelectrode 6, as shown in FIG. 10, to allow significant reductions inmaterial and processing cost although being lower in photoelectricconversion efficiency than the currently available silicon solar cell.

However, the semiconductor electrode 3 is arranged on alight-transmitting substrate 2 with a transparent conductive film 43,which functions as a light-transmitting collector electrode, beinginterposed between the light-transmitting substrate 2 and thesemiconductor electrode 3. The transparent conductive film 43 has ahigher resistance than that of a metallic film. The arrangement of sucha transparent conductive film 43 causes an increase in cell internalresistance to produce a substantial voltage drop even by the developmentof a slight electric current. Further, the transparent conductive film43 is generally applied to the light-transmitting substrate 2 bysputtering etc. so that it takes time and effort in the manufacturing ofthe dye-sensitized solar cell. The arrangement of the transparentconductive film 43 also causes a decrease in light transmissivity toreduce the amount of light reaching the semiconductor electrode 3 andresult in a lowering of photoelectric conversion efficiency.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve the above problems and aimsto provide a dye-sensitized solar cell capable of securing a lowerinternal resistance without the need to attach a light-transmittingcollector electrode and the like to a light-transmitting substrate onthe light incident side.

According to an aspect of the present invention, there is provided adye-sensitized solar cell, comprising: a first substrate having alight-transmitting property; a semiconductor electrode containing asensitizing dye and arranged in such a manner that a first surface ofthe semiconductor electrode faces the first substrate; a first collectorelectrode arranged on a second surface of the semiconductor electrode;an insulating layer arranged in contact with the first collectorelectrode; a catalytic electrode layer arranged in such a manner that afirst surface of the catalytic electrode layer faces the insulatinglayer; a second substrate arranged on a second surface of the catalyticelectrode layer; and an electrolyte material incorporated in thesemiconductor electrode, the first collector electrode and theinsulating layer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a dye-sensitized solar cell according toone preferred embodiment of the present invention.

FIG. 2 is a schematic view of a semiconductor electrode of thedye-sensitized solar cell.

FIG. 3 is a schematic view of the dye-sensitized solar cell, when havinga collector electrode partly embedded in the semiconductor electrode.

FIG. 4 is a schematic view showing one example of grid electrode patternof collector electrode arrangement.

FIG. 5 is a schematic view showing one example of comb electrode patternof collector electrode arrangement.

FIG. 6 is a schematic view showing one example of radial electrodepattern of collector electrode arrangement.

FIG. 7 is a schematic view of the dye-sensitized solar cell, when havinga catalytic electrode layer used as a positive terminal.

FIG. 8 is a schematic view of the dye-sensitized solar cell, when havinga substrate used as a positive terminal.

FIG. 9 is a schematic view of the dye-sensitized solar cell, whenprovided with an electrolyte material layer.

FIG. 10 is a schematic view of a dye-sensitized solar cell according tothe earlier technology.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, one preferred embodiment of the present invention will bedescribed below in detail with reference to FIGS. 1 to 10.

A dye-sensitized solar cell 1 according to one embodiment of the presentinvention includes a light-transmitting substrate 2, a semiconductorelectrode 3, a first collector electrode 41, an insulating layer 5, acatalytic electrode layer 6, a substrate 7 (7′) and an electrolytematerial 8 as shown in FIG. 1.

The light-transmitting substrate 2 is not particularly restricted aslong as it shows a light-transmitting property in a wavelength rangewhere photoelectric power generation is possible. The material of thelight-transmitting substrate 2 can be selected as appropriate. As thelight-transmitting substrate 2, there may be used a sheetsubstrate ofglass, resin, ceramic or the like. The kind of the glass is notparticularly restricted. Examples of the glass include soda glass,borosilicate glass, aluminosilicate glass, aluminoborosilicate glass,silica glass and soda-lime glass. The kind of the resin is notparticularly restricted. Examples of the resin sheet include sheets ofpolyesters such as polyethylene terephthalate and polyethylenenaphthalate and other sheets of polyphenylene sulfides, polycarbonates,polysulfones and polyethylidene norbornenes. The kind of the ceramic isnot also restricted. Examples of the ceramic include high purityalumina.

The light-transmitting substrate 2 varies in thickness depending on thematerial thereof. The thickness of the light-transmitting substrate 2 isnot particularly restricted but is desirably of such a thickness thatthe substrate 2 is capable of maintaining its light-transmittingproperty.

Herein, the light-transmitting property means that the transmissivity ofvisible light having a wavelength of 400 to 900 nm as expressed by thefollowing equation is 10% or higher. The light transmissivity ispreferably in a range of 60% or higher, more preferably 85% or higher.The meaning of the light-transmitting property and the desirable rangeof the light transmissivity are hereinafter the same throughout thedescription.Transmissivity (%)=(the amount of transmitted light/the amount ofincident light)×100

The semiconductor electrode 3 is arranged with a first surface thereoffacing the light-transmitting substrate 2 and has a sensitizing dye 31and a electrode body 32 made of a semiconductor material as shown inFIG. 2. The semiconductor electrode 3 may or may not be in contact withthe light-transmitting substrate 2.

As the sensitizing dye 31, there may be used a complex dye or an organicdye for improved photoelectric conversion. Examples of the complex dyeinclude metal complex dyes. Examples of the organic dye includepolymethine dyes and merocyanine dyes. Specific examples of the metalcomplex dyes include ruthenium complex dyes and osmium complex dyes.Among others, especially preferred are ruthenium complex dyes. In orderto extend the photoelectric conversion wavelength range of thesensitizing dye and thereby obtain an improvement in photoelectricconversion efficiency, two or more kinds of sensitizing dye compoundshaving different photoelectric conversion wavelength ranges can be usedin combination. In this case, it is desirable to select the kinds andquantity ratio of the sensitizing dye compounds to be used incombination according to the wavelength range and intensity distributionof irradiation light. Further, the sensitizing dye 31 preferablyincludes a functional group for bonding to the semiconductor electrode3. Examples of the functional group include a carboxyl group, a sulfonicgroup and a cyano group.

The electrode body 32 can be made of a metal oxide material, a metalsulfide material or the like. Examples of the metal oxide materialinclude titanium oxide, tin oxide, zinc oxide and niobium oxide such asniobium pentoxide, tantalum oxide and zirconia. As the metal oxidematerial, there may also be used double oxide such as strontiumtitanate, calcium titanate and barium titanate. Examples of the metalsulfide material include zinc sulfide, lead sulfide and bismuth sulfide.Among others, especially preferred is titanium oxide.

The preparation method of the electrode body 32 is not particularlyrestricted. The electrode body 32 can be prepared by, for example,applying a paste containing fine particles of metal oxide or metalsulfide to a surface of the insulating layer 5 or the first collectorelectrode 41, and then, sintering the paste. The paste applicationprocess is not also particularly restricted and is exemplified by ascreen printing process, a doctor blade process, a squeegee process, aspin coat process and the like. The thus-prepared electrode body 32 isin the form of an aggregate in which the fine particles areagglomerated. Alternatively, the electrode body 32 may be prepared byapplying a colloid in which fine particles of metal oxide or metalsulfide are dispersed together with a small quantity of organic polymerto the surface of the insulating layer 5 or the first collectorelectrode 41, and then, removing the organic polymer by heatdecomposition. The colloid can be applied by any process technique suchas a screen printing process, a doctor blade process, a squeegee processor a spin coat process. The thus-prepared electrode body 32 is also inthe form of an aggregate in which the fine particles are agglomerated.

In this way, the electrode body 32 is generally in fine particleaggregate form. The average diameter of the fine particles, as measuredby X-ray diffraction, is not particularly restricted and desirablyranges from 5 to 100 nm, especially 10 to 50 nm.

The thickness of the semiconductor electrode 3 is not particularlyrestricted and can be adjusted to 0.1 to 100 μm. It is desirable thatthe thickness of the semiconductor electrode 3 ranges from 1 to 50 μm,especially 2 to 40 μm, more specifically 5 to 30 μm. When the thicknessof the semiconductor electrode 3 is in the range of 0.1 to 100 μm, it ispossible to allow light transmission substantially throughout thesemiconductor electrode 3 for improved photoelectric conversion.

Further, the semiconductor electrode 3 is desirably subjected to heattreatment in order to increase the strength of the semiconductorelectrode 3 and the adhesion of the semiconductor electrode 3 with theinsulating layer 5 or the first collector electrode 41. The temperatureand time of the heat treatment are not particularly restricted. It isdesirable to control the heat treatment temperature to within 40 to 700°C., especially 100 to 500° C., and to control the heat treatment time towithin 10 minutes to 10 hours, especially 20 minutes to 5 hours.

The method of adhering the sensitizing dye 31 to the electrode body 32is not particularly restricted. The sensitizing dye 31 can be adhered tothe electrode body 32 by, for example, immersing the electrode body 32into a solution in which the sensitizing dye 31 is dissolved with anorganic solvent, impregnating the electrode body 32 with the solution,and then, removing the organic solvent. Alternatively, the sensitizingdye 31 may be adhered to the electrode body 32 by applying a solution inwhich the sensitizing dye 31 is dissolved with an organic solvent to theelectrode body 32, and then, removing the organic solvent. The solutionapplication process is herein exemplified by a wire bar process, a slidehopper process, an extrusion process, a curtain coating process, a spincoat process, a spray coat process and the like. The solution canalternatively be applied by a printing process such as an offsetprinting process, a gravure printing process or a screen printingprocess.

The adhesion amount of the sensitizing dye 31 preferably ranges from0.01 to 1 mmol, especially 0.5 to 1 mmol, per 1 g of the electrode bodyof the semiconductor electrode 3. When the adhesion amount of thesensitizing dye 31 is in the range of 0.01 to 1 mmol, the semiconductorelectrode 3 is able to attain high photoelectric conversion efficiency.If some of the sensitizing dye 31 exists free around the electrodewithout being adhered to the electrode body 32, the photoelectricconversion efficiency of the semiconductor electrode 3 may be lowered.It is thus desirable to remove excessive sensitizing dye by washing theelectrode body 32 after the process of adhering the sensitizing dye 31to the electrode body 32. The excessive sensitizing dye can be removedby washing with an organic solvent such as a polar solvent e.g.acetonitrile or an alcohol solvent through the use of a washing bath. Inorder to adhere a great amount of sensitizing dye to the electrode body32, the electrode body 32 is preferably subjected to heating before theimpregnation or application process. In this case, it is furtherpreferred that the impregnation or application process is performed attemperatures of 40 to 80° C. immediately after the heat treatment andbefore the electrode body 32 reaches an ambient temperature, in order toavoid water from being adsorbed onto a surface of the electrode body 32.

The first collector electrode 41 is arranged on a second surface of thesemiconductor electrode 3 so as to receive electrodes from thesemiconductor electrode 3 and discharge the electrons out of the solarcell. The material of the first collector electrode 41 can be selectedas appropriate. As the material of the first collector electrode 41,metal, conductive oxide and carbon are usable. Examples of the metalinclude tungsten, titanium, nickel, platinum, gold, copper, aluminum,rhodium and indium. Among others, tungsten is preferred. Examples of theconductive oxide include tin oxide, fluorine-doped tin oxide (FFO),indium oxide, tin-doped indium oxide (ITO) and zinc oxide.

The form of the first collector electrode 41 is not particularlyrestricted and can be selected as appropriate in such a manner as toallow the first collector electrode 41 to collect electrons from allover the semiconductor electrode 3. For example, the first collectorelectrode 41 may be provided in sheet form, in linear form (e.g. stripform or bar form) of predetermined pattern or in a combination thereof.The first collector electrode 41 can alternatively be arranged on adifferent place from the second surface of the semiconductor electrode3, i.e., on the opposite surface of the semiconductor electrode 3(facing the light-transmitting substrate 2) or the side surface of thesemiconductor electrode 3. As illustrated by an example in FIG. 3, apart or the whole of the first collector electrode 41 may be embedded inthe semiconductor electrode 3.

In the case where the first collector electrode 41 is in sheet form, itis required that the first collector electrode 41 be formed into aporous medium in order for the electrolyte material 8 to be distributedbetween the semiconductor electrode 3 and the catalytic electrode layer6 for ion migration. The porosity of such a porous medium, as measuredby electron microscopic analysis, is not particularly restricted and canrange from 2 to 40%, especially 10 to 30%, more especially 15 to 25%.When the porosity of the porous medium is in the range of 10 to 30%, itis possible to distribute the electrolyte material 8 adequately throughthe porous medium without causing a deterioration in charge collectionefficiency.

The first collector electrode 41 in such porous sheet form can beprepared by applying a coating of paste containing a metal componentsuch as tungsten, titanium or nickel and a pore-forming oxide materialsuch as alumina and then sintering the paste coating.

In the case where the first collector electrode 41 is in linear form,the arrangement pattern of the first collector electrode 41 can beselected as appropriate. Examples of the electrode pattern include agrid pattern (see FIG. 4), a comb pattern (see FIG. 5) and a radialpattern (see FIG. 6). The first collector electrode 41 may be formed ina single kind of pattern, or in a combination of a plurality of patternsof the same kind or different kinds. Examples of the grid patterninclude those having pattern units in the shapes of triangles (a regulartriangle and any other triangles), quadrangles (a regular quadrangle andany other quadrangles), pentagons (a regular pentagon and any otherpentagons), hexagons (a regular hexagon and any other hexagons), circles(including an elliptic circle and any other distorted circles) and thelike. The width and thickness of the first collector electrode 41 inlinear form are not particularly restricted and can be selected asappropriate in view of the electrical resistance, cost and the like.

The preparation method of the first collector electrode 41 in suchlinear form is not particularly restricted. For example, the firstcollector electrode 41 can be prepared by depositing a metal e.g.tungsten, titanium or nickel by a physical vapor deposition process suchas magnetron sputtering or electron-beam vapor deposition using a maskof predetermined pattern, and then, patterning the deposit by aphotolithographic process. Alternatively, the first collector electrode41 may be prepared by patterning a paste containing a metal component bya screen printing process etc. and sintering the paste. Examples of themetal usable in vapor phase deposition include copper in addition totungsten, titanium and nickel. Among others, tungsten, titanium andnickel having a high corrosion resistance are preferred as thedeposition metal. As the metal contained in the paste, there may also beused tungsten, titanium, nickel and copper. Tungsten, titanium andnickel having a high corrosion resistance are preferred as the pastemetal.

There may be additionally provided a second collector electrode 42 on afirst surface of the catalytic electrode layer 6 so as to feed electronsinto the catalytic electrode layer 6 from the outside of the solar cell.The material of the second collector electrode 42 can be selected as isthe case with the material of the first collector electrode 42. The formof the second collector electrode 42 can be selected in such a manner asto allow the second collector electrode 42 to collect electrons from allover the catalytic electrode layer 6. For example, the second collectorelectrode 42 may be provided in sheet form, in linear form (e.g. stripform or bar form) of predetermined pattern or in a combination thereof.The second collector electrode 42 can alternatively be arranged on adifferent place from the first surface of the catalytic electrode layer6, i.e., on the opposite surface of the catalytic electrode layer 6(facing the substrate 7) or the side surface of the catalytic electrodelayer 6. Further, a part or the whole of the second collector electrode42 can be embedded in the catalytic electrode layer 6. In the case wherethe second collector electrode 42 is in sheet form, the second collectorelectrode 42 may or may not be formed into a porous medium without theneed for the second collector electrode 42 to distribute therethroughthe electrode material 8 in contrast to the first collector electrode41. In the case where the second collector electrode 42 is in linearform, the arrangement pattern of the second collector electrode 42 canbe selected as appropriate as in the case with the first collectorelectrode 41.

The first collector electrode 41 and the second collector electrode 42do not necessarily show light-transmitting properties in ordinary casesbut may have light-transmitting properties. Each of the first and secondcollector electrodes 41 and 42, when having a light-transmittingproperty, can be in the form of a thin film of metal (limited to thatwhich is formable into a thin film), conductive oxide or carbon.Alternatively, the first and second collector electrodes 41 and 42 maybe in linear form of predetermined pattern or in a combination ofthin-film form and linear form when having light-transmittingproperties.

The insulating layer 5 is provided as a separator to prevent theoccurrence of inability to obtain power from the dye-sensitized solarcell 1 upon contact of the semiconductor electrode 3 and the firstcollector electrode 41 with the catalytic electrode layer 6 and thesecond collector electrode 42 and is formed into a porous medium so asto distribute therethrough the electrolyte material 8.

The material of the insulating layer 5 is not particularly restricted.There may be used ceramic, resin and glass as the material of theinsulating layer 5. The insulating layer 5 is desirably formed ofceramic. The kind of the ceramic is not particularly restricted. Variousceramic materials such as oxide ceramic, nitride ceramic and carbideceramic are usable. Examples of the oxide ceramic include alumina,mullite and zirconia. Examples of the nitride ceramic include siliconnitride, sialon, titanium nitride and aluminum nitride. Examples of thecarbide ceramic include silicon carbide, titanium carbide and aluminumcarbide. Among others, alumina, silicon nitride and zirconia arepreferred. Especially preferred is alumina.

The form of the insulating layer 5 can be selected as appropriate so asto prevent contact of the semiconductor electrode 3 and the firstcollector electrode 41 with the catalytic electrode layer 6 and thefirst collector electrode 42. For example, the insulating layer 5 may beprovided in sheet form, in linear form (e.g. strip form or bar form) ofpredetermined pattern or in a combination thereof as is the case withthe first collector electrode 41.

When the insulating layer 5 is of a porous medium, the porosity of theinsulating layer 5, as measured by electron microscopic analysis, is notparticularly restricted and desirably ranges from 2 to 40%, especially10 to 30%, more especially 15 to 25%. When the porosity of theinsulating layer 5 is in the range of 10 to 30%, the electrolytematerial 8 can be easily charged and migrated through the insulatinglayer 5 without impairment of the operation of the solar cell 1.

The thickness of the insulating layer 5 is not particularly restrictedand varies depending even on the manufacturing method of thedye-sensitized solar cell 1. In the case of manufacturing thedye-sensitized solar cell 1 by stacking a laminate in which thesubstrate 7, the catalytic electrode layer 6, the insulating layer 5,the first collector electrode 41 and the semiconductor electrode 3 arelaminated together in order of mention onto the light-transmittingsubstrate 2, the thickness of the insulating layer 5 can be adjusted to0.5 to 20 μm, especially 1 to 10 μm, more especially 2 to 5 μm. When thethickness of the insulting layer 5 is in the range of 0.5 to 20 μm inthat case, it is possible to establish electrical insulation between theside of the semiconductor electrode 3 and the side of the catalyticelectrode layer 6.

The insulating layer 5 can be prepared by applying a paste containing aceramic component and the like to the surface of the catalytic electrodelayer 6 by a screen printing process etc. and sintering the paste for apredetermined time at a predetermined temperature. Alternatively, theinsulating layer 5 may be prepared through the deposition of ceramice.g. alumina, silicon nitride or zirconia onto the surface of thecatalytic electrode layer 6 by a physical vapor deposition process suchas magnetron sputtering or electron-beam vapor deposition.

The catalytic electrode layer 6 can be made of either a catalyticallyactive material or at least one of metals and conductive oxides andresins containing therein a catalytically active material. Examples ofthe catalytically active material include noble metals such as platinumand rhodium and carbon black. (Silver is not suitable for use in thecatalytic electrode layer 6 due to its low resistance to corrosion by anelectrolyte etc. For the same reason, silver is not suitable for use inany portion that may come into contact with an electrolyte etc.) Thesematerials also have conducting properties. It is preferable that thecatalytic electrode layer 6 be made of noble metal having catalyticactivity and electrochemical stability. Especially preferred isplatinum, which has high catalytic activity and is less prone to beingdissolved by an electrolytic solution.

In the case of using any of the metals, conductive oxides and conductiveresins showing no catalytic activity, the metals usable in the catalyticelectrode layer 6 are exemplified by aluminum, copper, chrome, nickeland tungsten and the conductive resins usable in the catalytic electrodelayer 6 are exemplified by polyaniline, polypyrrole and polyacethylene.The conductive resins are also exemplified by resin compositionsprepared by mixing conductive materials into nonconductive resinmaterials. The resin material is not particularly restricted and can beeither a thermoplastic resin or a thermosetting resin. Examples of thethermoplastic resin include thermoplastic polyester resins, polyamideresins, polyolefin resins and polyvinyl chloride resins. Examples of thethermosetting resin include epoxy resins, thermosetting polyester resinsand phenol resins. The conductive material is not also particularlyrestricted. Examples of the conductive material include carbon black,metals such as copper, aluminum, nickel, chromium and tungsten andconductive polymers such as polyaniline, polypyrrole and polyacethylene.As the conductive materials, especially preferred are noble metal andcarbon black each having conductive properties and catalytic activities.These conductive materials can be used solely or in combination thereof.In the case of using any of the metals, conductive oxides and conductiveresins showing no catalytic activity, it is further desirable that thecatalytically active material be contained in an amount of 1 to 99 partsby mass, especially 50 to 99 parts by mass, per 100 parts by mass of thecatalytically inactive metal, conductive oxide and/or conductive resinmaterial.

In this way, the catalytic electrode layer 6 can be prepared from eitherthe catalytically active and electrically conductive material or atleast one of the metals, the conductive oxides and the conductive resinscontaining the catalytically active material. The catalytic electrodelayer 6 may be a layer of one kind of material or a mixed layer of twoor more kinds of materials. Further, the catalytic electrode layer 6 mayhave a single layer structure or a multilayer structure including morethan one of metal layers, conductive oxide layers, conductive resinlayers and mixed layers of two or more of metals, conductive oxides andconductive resins.

The thickness of the catalytic electrode layer 6 is not particularlyrestricted and can be adjusted to 3 nm to 10 μm, especially 3 nm to 2μm. When the thickness of the catalytic electrode layer 6 is in therange of 3 nm to 10 μm, it is possible to decrease the resistance of thecatalytic electrode layer 6 to a sufficiently low degree.

In the case of the catalytic electrode layer 6 being of thecatalytically active material, the catalytic electrode layer 6 can beprepared by applying a paste containing fine particles of thecatalytically active material to the surface of the substrate 7 or, whenthe second collector electrode 42 is provided, to the surface of thesecond collector electrode 42. In the case of the catalytic electrodelayer 6 being of any metal or conductive oxide containing thecatalytically active material, the catalytic electrode layer 6 can beprepared in the same manner as in the case of the catalytic electrodelayer 6 being of the catalytically active material. The pasteapplication process is exemplified by various process techniques such asa screen printing process, a doctor blade process, a squeegee processand a spin coat process. Alternatively, the catalytic electrode layer 6may be prepared through the deposition of the metal or the like to thesurface of the substrate 7 by a sputtering process, a vapor depositionprocess, an ion plating process or the like. In the case of thecatalytic electrode layer 6 being of the conductive resin containing thecatalytically active material, the catalytic electrode layer 6 can beprepared by kneading the conductive resin with the catalytically activematerial in powdery or fibrous form through the use of a kneading devicesuch as a Banbury mixer, an internal mixer or an open roll, molding thekneaded substance into a film, and then, bonding the film to thesurfaces of the substrate 7 and the like. The catalytic electrode layer6 may alternatively be prepared by dissolving or dispersing the resincomposition into a solvent, applying the thus-obtained solution ordispersoid to the surfaces of the substrate 7 and the like, drying toremove the solvent, and then, heating as required. The catalyticelectrode layer 6, when being a mixed layer, is prepared by any of theabove catalyst layer preparation methods according to the kinds of thematerial components thereof.

The catalytic electrode layer 6 can be also used as a collectorelectrode. For example, the function of the collector electrode may beimparted to the catalytic electrode layer 6 by exposing the catalyticelectrode layer 6 to the outside in such a manner as to allow aconnection of a lead wire etc. to the catalytic electrode layer 6 asshown in FIG. 7.

The substrate 7 may or may not have a light-transmitting property.

The substrate 7 with no light-transmitting property can be made ofceramic, metal, resin or glass.

The substrate 7, when prepared using ceramic, is so high in strength asto function as a supporting substrate and provide the dye-sensitizedsolar cell 1 with excellent durability. A ceramic material for theceramic substrate is not particularly restricted. Various ceramicmaterials such as oxide ceramic, nitride ceramic and carbide ceramic areusable. Examples of the oxide ceramic include alumina, mullite andzirconia. Examples of the nitride ceramic include silicon nitride,sialon, titanium nitride and aluminum nitride. Examples of the carbideceramic include silicon carbide, titanium carbide and aluminum carbide.As the ceramic material, preferred are aluminum, silicon nitride andzirconia. Alumina is especially preferred.

The substrate 7, when prepared using metal, is also so high in strengthas to function as a supporting substrate and provide the dye-sensitizedsolar cell 1 with excellent durability. The internal resistance of thedye-sensitized solar cell 1 can be lowered by providing the substrate 7′of metal as shown in FIG. 8 and thereby securing high charge collectionefficiency owing to the conducting property of the metal substrate 7 initself even though the second collector electrode 42 is not provided.This substrate metal can be selected as appropriate. Examples of thesubstrate metal include tungsten, titanium, nickel, noble metals such asplatinum and gold and copper.

In the case of the substrate 7 having no light-transmitting property,the thickness of the substrate 7 is not particularly restricted and canbe adjusted to 100 μm to 5 mm, especially 500 μm to 5 mm, moreespecially 800 μm to 5 mm, or 500 μm to 2 mm. When the thickness of thesubstrate 7 is in the range of 100 μm to 5 mm, especially 800 μm to 5mm, the substrate 7 is able to attain high strength and function as asupporting substrate so as to provide the dye-sensitized solar cell 1with excellent durability.

The substrate 7 with a light-transmitting property can be formed of asheet of glass, resin or the like as in the case of thelight-transmitting substrate 2. In the case of the substrate 7 being ofthe resin sheet, there may be used a thermosetting resin such aspolyester, polyphenylene sulfide, polycarbonate, polysulfone andpolyethylidene norbornene as the material of the resin sheet.

In the case of the substrate 7 having a light-transmitting property, thesubstrate 7 varies in thickness depending on the material thereof. Thethickness of the substrate 7 is not particularly restricted and isdesirably of such a thickness that the above-defined transmissivityranges from 60 to 99%, especially from 85 to 99%.

The electrolyte material 8 is incorporated in the semiconductorelectrode 3, the first collector electrode 41 and the insulating layer 5so as to allow ion conduction between the semiconductor electrode 3 andthe catalytic electrode layer 6. This electrolyte material 8 can beprepared from an electrolyte solution. This electrolyte solutiongenerally contains a solvent and various additives in addition to theelectrolyte material 8. Examples of the electrolyte material 8 include:(1) I₂ and an iodide; (2) Br₂ and a bromide; (3) a metal complex such asa ferrocyanide-ferricyanide complex or a ferrocene-ferricinium ioncomplex; (4) a sulfur compound such as sodium polysulfide oralkylthiol-alkyldisulfide; (5) a viologen dye; and (6)hydroquinone-quinone. As the iodide of the electrolyte (1), there can beused metal iodides such as LiI, NaI, KI, CsI and CaI₂, quaternaryammonium iodides such as tetraalkylammonium iodide, pyridinium iodideand imidazolium iodide and the like. As the bromide of the electrolyte(2), there can be used metal bromides such as LiBr, NaBr, KBr, CsBr andCaBr₂, quaternary ammonium bromides such as a tetraalkylammonium bromideand pyridinium bromide and the like. Among these electrolyte materials,especially preferred is a combination of I₂ and LiI or the quaternaryammonium iodide such as pyridinium iodide or imidazolium iodide. Theseelectrolyte materials may be used solely or in combination thereof.

The solvent of the electrolyte solution is preferably a solvent havinglow viscosity, high ionic mobility and sufficient ionic conductance.Examples of such a solvent include: (1) carbonates such as ethylenecarbonate and propylene carbonate; (2) heterocyclic compounds such as3-methyl-2-oxazolidinone; (3) ethers such as dioxane and diethyl ether;(4) chain ethers such as ethylene glycol dialkylethers, propylene glycoldialkylethers, polyethylene glycol dialkylethers and polypropyleneglycol dialkylethers; (5) monoalcohols such as methanol, ethanol,ethylene glycol monoalkylethers, propylene glycol monoalkylethers,polyethylene glycol monoalkylethers and polypropylene glycolmonoalkylethers; (6) polyalcohols such as ethylene glycol, propyleneglycol, polyethylene glycol, polypropylene glycol and glycerin; (7)nitriles such as acetonitrile, glutarodinitrile, methoxyacetonitrile,propionitrile and benzonitrile; and (8) aprotic polar solvents such asdimethylsulfoxide and sulfolane.

Each of one or two or more of the pairs of the light-transmittingsubstrate 2 and the semiconductor electrode 3, of the first collectorelectrode 41 and the insulating layer 5 and of the pair of theinsulating layer 5 and the catalytic electrode layer 6 may be arrangedto have contact or space therebetween in the dye-sensitized solar cell 1as shown in FIG. 9. When the space between these cell components isfilled with the electrolyte material 8 to form an electrolyte layer 81,the solar cell 1 is able to function properly. The electrolyte material8 may be filled into the whole of the space or be filled into the majorportion of the space with the remaining portion of the space left free.

Further, the dye-sensitized solar cell 1 has a seal 91 betweencircumferences of the light-transmitting substrate 2 and the substrate 7so as to avoid a loss of electrolyte material 8. The seal 91 can beformed of a resin or the like. Examples of the resin includethermosetting resins such as epoxy resins, urethane resins, polyimideresins and thermosetting resins such as thermosetting polyester resins.The seal 91 may alternatively be formed of glass. It is desirable thatthe seal 91 be of glass especially when the solar cell requireslong-term durability.

As described above, there is no need in the dye-sensitized solar cell 1to provide a light-transmitting collector electrode to thelight-transmitting substrate 2 on the light incident side. It istherefore possible to lower the internal resistance of thedye-sensitized solar cell 1 with the use of the collector electrode 41of metal having a light shielding property and low resistance. It isalso possible to irradiating a large amount of light on thesemiconductor electrode 3 and improve the photoelectric conversionefficiency of the dye-sensitized solar cell 1 without the light amountbeing reduced by such a light-transmitting collector electrode.

When the substrate 7 is made of ceramic, the substrate 7 functions as asupporting substrate. The dye-sensitized solar cell 1 is thus able toattain excellent durability.

When the semiconductor electrode 3 is made of titanium oxide, thedye-sensitized solar cell 1 is able to obtain an improvement inphotoelectric conversion efficiency.

When the first collector electrode 41 is of a porous medium layer, thefirst collector electrode 41 allows the electrolyte material 8 to passtherethrough to the catalytic electrode layer 6 adequately. The firstcollector electrode 41 also allows the electrolyte material 8 to passtherethrough to the catalytic electrode layer 6 adequately, whileattaining an improvement in photoelectric conversion efficiency, whenthe planar configuration of the first collector electrode 41 is in agrid pattern, a comb pattern or a radial pattern.

The dye-sensitized solar cell 1 is made lower in internal resistance inthe case of the second collector electrode 42 being provided between thesubstrate 7 and the catalytic electrode layer 6. When the planarconfiguration of the second collector electrode 42 is in sheet form orin a grid pattern, a comb pattern or a radial pattern, thedye-sensitized solar cell 1 is able to obtain an improvement inphotoelectric conversion efficiency. The dye-sensitized solar cell 1 isable to obtain a further improvement in photoelectric conversionefficiency especially when the second collector electrode 42 is in sheetform.

EXAMPLES

The present invention will be described in more detail with reference tothe following examples of the dye-sensitized solar cell 1. It should behowever noted that the following examples are only illustrative and notintended to limit the invention thereto.

Example 1

In Example 1, a dye-sensitized solar cell 1 was manufactured bylaminating solar cell components successively from the side of asubstrate 7 by the following procedures.

(1) Production of Sintered Laminate

A slurry was prepared by mixing 100 parts by mass of an aluminum powderof 99.9 mass % purity with 5 parts by mass of a mixed powder ofmagnesia, calcia and silica as a sintering aid, 2 parts by mass of abinder and a solvent. Using this slurry, an alumina green sheet for asubstrate 7 having a length of 100 mm, a width of 100 mm and a thicknessof 2 mm was produced by a doctor blade process. Next, a conductive filmfor a second collector electrode 42 was provided on a surface of thealumina green sheet through the application of a paste containingtungsten particles of 1 to 10 μm in diameter by a screen printingprocess. A conductive film for a catalytic electrode layer 6 having athickness of 500 nm was provided on a surface of the above-appliedconductive film by a screen printing process using a platinum-containingmetalized ink. An alumina green sheet for an insulating layer 5 wasfurther formed through the application of the alumina slurry by a screenprinting process. Then, a conductive film for a first collectorelectrode 41 was provided on the aluminum green sheet layer through theapplication of the same tungsten-containing paste as above by a screenprinting process. The thus-obtained green laminate was integrallysintered at 1500° C. in a reducing atmosphere, thereby yielding asintered laminate.

(2) Production of Semiconductor Electrode 3

A titanium electrode layer (as an electrode body 32) having a length of90 mm, a width of 90 mm and a thickness of 20 μm was formed on a surfaceof the sintered laminate located on the side of the catalytic electrodelayer 6, by applying a paste containing titania particles by a screenprinting process, drying at 120° C. for 1 hour and sintering at 480° C.for 30 minutes. The laminate was then immersed in an ethanol solution ofruthenium complex (available under the trade name of “535bis-TBA” fromSolaronix) for 10 hours, so as to adhere the ruthenium complex as asensitizing dye 31 having a light absorption wavelength of 400 to 600 nmto the sintered titanium particles as partly enlarged in FIG. 2 andthereby complete a semiconductor electrode 3.

(3) Sealing of Electrolyte Material 8

A thermoplastic adhesive sheet, for a joint 91, having a thickness of 60μm (available under the trade name of “SX1170-60” from Solaronix) wasprovided at a location on a surface of the alumina substrate 7 of thesintered laminate on which the catalytic electrode layer 6 and the likehad been formed and around the catalytic electrode layer 6. After that,a soda glass substrate (as a light-transmitting substrate 2) having alength of 100 mm, a width of 100 mm and a thickness of 1 mm was arrangedin such a manner as to face the semiconductor electrode 3. Thethus-obtained laminate was placed on a hot plate whose temperature hadbeen adjusted to 100° C., with the alumina substrate 7 being directeddownward, and heated for 5 minutes. The joint 91 was established betweenthe soda glass substrate 2 and the alumina substrate 7 by heating. Anelectrolyte material 8 was incorporated into the semiconductor electrode3, the first collector electrode 41 and the insulating layer 5 byinjecting an iodine electrolytic solution (available under the tradename of “Iodolyte PN-50” from Solaronix) through unjoined electrolytesolution injection holes. The injected iodine electrolytic solution wasfilled into structural voids in the first collector electrode 41 and theinsulating layer 5 and migrated to reach the surface of the catalyticelectrode layer 6. After that, the injection holes were sealed with thesame adhesive as above. The dye-sensitized solar cell 1 shown in FIG. 1was then completed.

(4) Performance Evaluation of Dye-sensitized Solar Cell 1

Artificial sunlight was irradiated onto the dye-sensitized solar cell 1produced by the above procedures (1) to (3) with an intensity of 100mW/cm² by means of a solar simulator whose spectrum had been adjusted toAM 1.5. The dye-sensitized solar cell 1 characteristically showed aconversion efficiency of 6.8%.

Example 2

In Example 2, a dye-sensitized solar cell 1 having a first collectorelectrode 41 in a grid pattern was manufactured by the followingprocedures.

(1) Production of Sintered Laminate

An alumina green sheet for a substrate 7 having a length 100 mm, a widthof 100 mm and a thickness of 2 mm was prepared in the same manner as inExample 1. A conductive film for a second collector electrode 42 wasprovided on a surface of the alumina green sheet through the applicationof the same tungsten-containing paste as above by a screen printingprocess. A conductive film for a catalytic electrode layer 6 having athickness of 500 nm was provided on a surface of the above-appliedconductive film by a screen printing process using a platinum-containingmetalized ink. An alumina green sheet for an insulating layer 5 wasfurther formed through the application of the alumina slurry by a screenprinting process. Then, a conductive film for a first collectorelectrode 41 was provided on the aluminum green sheet layer through theapplication of the same tungsten-containing paste as above by a screenprinting process. Herein, the conductive film had a grid pattern ofsubstantially regular quadrangle pattern units with an opening rate of20%. The thus-obtained green laminate was integrally sintered at 1500°C. in a reducing atmosphere, thereby yielding a sintered laminate.

(2) Production of Semiconductor Electrode 3

A semiconductor electrode 3 was produced in the same manner as inExample 1.

(3) Sealing of Electrolyte Material 8

The dye-sensitized solar cell 1 was completed by providing a joint 91and then sealing an electrolyte material 8 in the same manner as inExample 1.

(4) Performance Evaluation of Dye-sensitized Solar Cell 1

Artificial sunlight was irradiated onto the dye-sensitized solar cell 1produced by the above procedures (1) to (3) with an intensity of 100mW/cm² by means of a solar simulator whose spectrum had been adjusted toAM 1.5. The dye-sensitized solar cell 1 characteristically showed aconversion efficiency of 8.0%. The evaluation result of Example 2 was asfavorable as that of Example 1.

Comparative Example

In Comparative Example, a dye-sensitized solar cell having alight-transmitting conductive layer 43 arranged on a light-transmittingsubstrate 2, as shown in FIG. 10, was manufactured by the followingprocedures.

(1) Production of Sintered Laminate

An alumina green sheet for a substrate 7 having a length of 100 mm, awidth of 100 mm and a thickness of 2 mm was prepared in the same manneras in Example 1. Next, a conductive film for a second collectorelectrode 42 was provided on a surface of the alumina green sheetthrough the application of the same tungsten-containing paste as aboveby a screen printing process. A conductive film for a catalyticelectrode layer 6 having a thickness of 500 nm was then provided on asurface of the above-applied conductive film by a screen printingprocess using a platinum-containing metalized ink. The thus-obtainedgreen laminate was integrally sintered at 1500° C. in a reducingatmosphere, thereby yielding a sintered laminate.

(2) Production of Laminate with Light-Transmitting Substrate

A glass substrate having a length of 100 mm, a width of 100 mm and athickness of 1 mm was prepared as a light-transmitting substrate 2. Alight-transmitting conductive layer 43 of fluorine-doped tin oxidehaving a thickness of 500 nm was provided on a surface of the substrate2 by a RF sputtering process. A titanium electrode layer (as anelectrode body) was subsequently formed on a surface of thelight-transmitting conductive layer 43 by applying the sametitania-containing paste as above by screen printing, drying at 120° C.for 1 hour and sintering at 480° C. for 30 minutes. A semiconductorelectrode 3 was then completed by immersing the laminate in the sameruthenium complex ethanol solution as above for 10 hours and therebyadhering a ruthenium complex sensitizing dye 31 to the electrode layer.

(3) Manufacturing of Dye-sensitized Solar Cell

The same adhesive sheet as above was provided to a surface portion ofthe alumina substrate 7 of the sintered laminate on which the catalyticelectrode layer 6 had not been formed. The light-transmitting substratelaminate was arranged in such a manner that the semiconductor electrode3 and the catalytic electrode layer 6 faced each other. Thethus-obtained laminate was placed on a hot plate whose temperature hadbeen adjusted to 100° C., with the alumina substrate 7 being directeddownward, and heated for 5 minutes to form a joint 91 between thelight-transmitting substrate 2 and the aluminum substrate 7. The sameiodine electrolytic solution as above was injected through unjoinedinjection holes. After that, the injection holes were sealed with thesame adhesive as above. The dye-sensitized solar cell shown in FIG. 10was then completed.

(4) Comparisons with Examples

The performance of the dye-sensitized solar cell of Comparative Examplewas evaluated in the same manner as in Example 1. The solar cell ofComparative Example showed a conversion efficiency of 6.2%. It is thusobvious that the solar cell of Comparative Example was lower inperformance than those of Examples 1 and 2.

Although the present invention has been described with reference to thespecific embodiments of the invention, the invention is not limited tothe above-described embodiments. Various modification and variation ofthe embodiments described above will occur to those skilled in the artin light of the above teaching. For example, there may alternatively beused, as the electrolyte material 8, an ionic liquid of nonvolatileimidazolium salt, a gelated product thereof or a solid such as copperiodide or copper thiocyanate. Although the first collector electrode 41,the insulating layer 5 and the second collector electrode 42 are madeporous in the above examples, the first collector electrode 41, theinsulating layer 5 and the second collector electrode 42 are not limitedto those of the above examples. As shown in FIGS. 4 to 6, each of thefirst collector electrode 41, the insulating layer 5 and the secondcollector electrode 42 may be provided in a line pattern.

1. A dye-sensitized solar cell, comprising: a first substrate having alight-transmitting property; a semiconductor electrode containing asensitizing dye and arranged in such a manner that a first surface ofthe semiconductor electrode faces the first substrate; a first collectorelectrode arranged on a second surface of the semiconductor electrode;an insulating layer arranged in contact with the first collectorelectrode; a catalytic electrode layer arranged in such a manner that afirst surface of the catalytic electrode layer faces the insulatinglayer; a second substrate arranged on a second surface of the catalyticelectrode layer; and an electrolyte material incorporated in thesemiconductor electrode, the first collector electrode and theinsulating layer.
 2. The dye-sensitized solar cell according to claim 1,wherein the second substrate is made of ceramic and/or metal.
 3. Thedye-sensitized solar cell according to claim 1, wherein thesemiconductor electrode is prepared from titanium oxide.
 4. Thedye-sensitized solar cell according to claim 1, wherein the firstcollector electrode is in the form of a porous layer.
 5. Thedye-sensitized solar cell according to claim 1, wherein the firstcollector electrode has a planar configuration in a grid pattern, combpattern or radial pattern.
 6. The dye-sensitized solar cell according toclaim 1, further comprising a second collector electrode between thesecond substrate and the catalytic electrode layer.
 7. Thedye-sensitized solar cell according to claim 6, wherein the secondcollector electrode has a planar configuration in a sheet form or in agrid pattern, a comb pattern or a radial pattern.